324 J. M. Ordway on Nitrates of Iron. 
In the first instance the action was apparently over in six 
minutes. In the next five cases all was quiet at the end of 
a, 
| wal 
fo 
g 
R 
= 
x) 
rm 
(a) 
cr 
eps 
o) 
5 
° 
gm 3 
oO 
rs 
— 
bo] 
= 
n, 
oo 
a 
oO 
be] 
mM 
Rm 
tq?) 
bar 
Lg 
° 
5 
oe 
o 
oo 
or 
cr 
bo 
oO 
5 
oO 
ms 
ae 
L oeiad 
=) 
Pa 
mediately becomes covered with a layer of nitrate insoluble in 
nitric acid. Thus Heldt says:'—“Die Haut von saltpetersauren 
I sate 
hindurch schimmert, ist unter einer guten Lupe deutlich zu 
erkennen.” film 
acid with the aid of a moderate heat. When iron has become 
passive while cold, the acid ought not to require heating beyond 
50 a oats the action recommence. But we have seen that 
even douing sometimes fails to remove passivit : 
When the ; tac 
oF Telations of iron is no more wonderful than the modification 
of the mechanical properties of steel by tempering, or the in- 
‘ a permanent magnetism in steel. - 
ae 22 follo "ing summary shows the results to be obtained by 
a. together iron and nitric acid under various conditions. 
~~ ~nere may be either no perceptible action or only amo 
mentary one, the we quickly becomin 
One, the y bec & passive. S 
a yy Supervenes most readily with ared acid and with 
yy 4 iron. And steel has its liability to become inert eD- 
chaft der Kérper, 5 108 woth: 
teed xe, tat , 
